Tharwat F. Tadros Applied Surfactants

Transcription

1 Tharwat F. Tadros Applied Surfactants

2 Further Titles of Interest L. L. Schramm Emulsions, Foams, and Suspensions Fundamentals and Applications 2005 ISBN E. Smulders Laundry Detergents 2002 ISBN H. M. Smith (Ed.) High Performance Pigments 2002 ISBN W. Herbst, K. Hunger Industrial Organic Pigments Production, Properties, Applications Third, Completely Revised Edition 2004 ISBN G. Buxbaum, G. Pfaff (Eds.) Industrial Inorganic Pigments Third, Completely Revised and Extended Edition 2005 ISBN K. Hunger (Ed.) Industrial Dyes Chemistry, Properties, Applications, 2003 ISBN

3 Tharwat F. Tadros Applied Surfactants Principles Applied and Surfactants Applications Principles and Applications

4 Author Prof. Dr. Tharwat F. Tadros 89 Nash Grove Lane Wokingham Berkshire RG40 4HE United Kingdom 9 This book was carefully produced. Nevertheless, author and publisher do not warrant the information contained therein to be free of errors. Readers are advised to keep in mind that statements, data, illustrations, procedural details or other items may inadvertently be inaccurate. Library of Congress Card No.: Applied for British Library Cataloguing-in-Publication Data: A catalogue record for this book is available from the British Library Bibliographic information published by Die Deutsche Bibliothek Die Deutsche Bibliothek lists this publication in the Deutsche Nationalbibliografie; detailed bibliographic data is available in the Internet at hhttp://dnb.ddb.dei WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim All rights reserved (including those of translation in other languages). No part of this book may be reproduced in any form by photoprinting, microfilm, or any other means nor transmitted or translated into machine language without written permission from the publishers. Registered names, trademarks, etc. used in this book, even when not specifically marked as such, are not to be considered unprotected by law. Printed in the Federal Republic of Germany Printed on acid-free paper Composition Asco Typesetters, Hong Kong Printing Strauss GmbH, Mörlenbach Bookbinding Litges & Dopf Buchbinderei GmbH, Heppenheim ISBN-13: ISBN-10:

5 Dedicated to our Grandchildren Nadia, Dominic, Theodore and Bruno

6 VII Contents Preface XIX 1 Introduction General Classification of Surface Active Agents Anionic Surfactants Carboxylates Sulphates Sulphonates Phosphate-containing Anionic Surfactants Cationic Surfactants Amphoteric (Zwitterionic) Surfactants Nonionic Surfactants Alcohol Ethoxylates Alkyl Phenol Ethoxylates Fatty Acid Ethoxylates Sorbitan Esters and Their Ethoxylated Derivatives (Spans and Tweens) Ethoxylated Fats and Oils Amine Ethoxylates Ethylene Oxide Propylene Oxide Co-polymers (EO/PO) Surfactants Derived from Mono- and Polysaccharides Speciality Surfactants Fluorocarbon and Silicone Surfactants Polymeric Surfactants Toxicological and Environmental Aspects of Surfactants Dermatological Aspects Aquatic Toxicity Biodegradability 16 References 16 2 Physical Chemistry of Surfactant Solutions Properties of Solutions of Surface Active Agents Solubility Temperature Relationship for Surfactants Thermodynamics of Micellization 26 Applied Surfactants: Principles and Applications. Tharwat F. Tadros Copyright WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim ISBN:

7 VIII Contents Kinetic Aspects Equilibrium Aspects: Thermodynamics of Micellization Phase Separation Model Mass Action Model Enthalpy and Entropy of Micellization Driving Force for Micelle Formation Micellization in Other Polar Solvents Micellization in Non-Polar Solvents Micellization in Surfactant Mixtures (Mixed Micelles) Surfactant Mixtures with no Net Interaction Surfactant Mixtures with a Net Interaction Surfactant Polymer Interaction Factors Influencing the Association Between Surfactant and Polymer Interaction Models Driving Force for Surfactant Polymer Interaction Structure of Surfactant Polymer Complexes Surfactant Hydrophobically Modified Polymer Interaction Interaction Between Surfactants and Polymers with Opposite Charge (Surfactant Polyelectrolyte Interaction) 46 References 50 3 Phase Behavior of Surfactant Systems Solubility Temperature Relationship for Ionic Surfactants Surfactant Self-Assembly Structure of Liquid Crystalline Phases Hexagonal Phase Micellar Cubic Phase Lamellar Phase Bicontinuous Cubic Phases Reversed Structures Experimental Studies of the Phase Behaviour of Surfactants Phase Diagrams of Ionic Surfactants Phase Diagrams of Nonionic Surfactants 66 References 71 4 Adsorption of Surfactants at the Air/Liquid and Liquid/Liquid Interfaces Introduction Adsorption of Surfactants Gibbs Adsorption Isotherm Equation of State Approach Interfacial Tension Measurements Wilhelmy Plate Method Pendent Drop Method 81

8 Contents IX Du Nouy s Ring Method Drop Volume (Weight) Method Spinning Drop Method 83 References 84 5 Adsorption of Surfactants and Polymeric Surfactants at the Solid/Liquid Interface Introduction Surfactant Adsorption Adsorption of Ionic Surfactants on Hydrophobic Surfaces Adsorption of Ionic Surfactants on Polar Surfaces Adsorption of Nonionic Surfactants Adsorption of Polymeric Surfactants at the Solid/Liquid Interface Adsorption and Conformation of Polymeric Surfactants at Interfaces Experimental Methods for Measurement of Adsorption Parameters for Polymeric Surfactants Amount of Polymer Adsorbed G Adsorption Isotherms Polymer Bound Fraction p Adsorbed Layer Thickness d and Segment Density Distribution r(z) Hydrodynamic Thickness Determination 110 References Applications of Surfactants in Emulsion Formation and Stabilisation Introduction Industrial Applications of Emulsions Physical Chemistry of Emulsion Systems Thermodynamics of Emulsion Formation and Breakdown Interaction Energies (Forces) Between Emulsion Droplets and their Combinations Mechanism of Emulsification Methods of Emulsification Role of Surfactants in Emulsion Formation Role of Surfactants in Droplet Deformation Selection of Emulsifiers Hydrophilic-Lipophilic Balance (HLB) Concept Phase Inversion Temperature (PIT) Concept Cohesive Energy Ratio (CER) Concept for Emulsifier Selection Critical Packing Parameter (CPP) for Emulsifier Selection Creaming or Sedimentation of Emulsions Creaming or Sedimentation Rates Prevention of Creaming or Sedimentation Flocculation of Emulsions Mechanism of Emulsion Flocculation 150

9 X Contents General Rules for Reducing (Eliminating) Flocculation Ostwald Ripening Emulsion Coalescence Rate of Coalescence Phase Inversion Rheology of Emulsions Interfacial Rheology Basic Equations for Interfacial Rheology Basic Principles of Measurement of Interfacial Rheology Correlation of Interfacial Rheology with Emulsion Stability Investigations of Bulk Rheology of Emulsion Systems Viscosity-Volume Fraction Relationship for Oil/Water and Water/Oil Emulsions Viscoelastic Properties of Concentrated O/W and W/O Emulsions Viscoelastic Properties of Weakly Flocculated Emulsions Experimental Methods for Assessing Emulsion Stability Assessment of Creaming or Sedimentation Assessment of Emulsion Flocculation Assessment of Ostwald Ripening Assessment of Coalescence Assessment of Phase Inversion 183 References Surfactants as Dispersants and Stabilisation of Suspensions Introduction Role of Surfactants in Preparation of Solid/Liquid Dispersions Role of Surfactants in Condensation Methods Role of Surfactants in Dispersion Methods Effect of Surfactant Adsorption Wetting of Powders by Liquids Rate of Penetration of Liquids Rideal Washburn Equation Measurement of Contact Angles of Liquids and Surfactant Solutions on Powders Structure of the Solid/Liquid Interface Origin of Charge on Surfaces Structure of the Electrical Double Layer Diffuse Double Layer (Gouy and Chapman) Stern Grahame Model of the Double Layer Electrical Double Layer Repulsion Van der Waals Attraction Total Energy of Interaction: Deryaguin Landau Verwey Overbeek (DLVO) Theory Criteria for Stabilisation of Dispersions with Double Layer Interaction 211

10 Contents XI 7.12 Electrokinetic Phenomena and the Zeta Potential Calculation of Zeta Potential Von Smoluchowski (Classical) Treatment Hückel Equation Henry s Treatment Measurement of Electrophoretic Mobility Ultramicroscopic Technique (Microelectrophoresis) Laser Velocimetry Technique General Classification of Dispersing Agents Surfactants Nonionic Polymers Polyelectrolytes Steric Stabilisation of Suspensions Interaction Between Particles Containing Adsorbed Polymer Layers Mixing Interaction G mix Elastic Interaction, G el Criteria for Effective Steric Stabilisation Flocculation of Sterically Stabilised Dispersions Properties of Concentrated Suspensions Characterisation of Suspensions and Assessment of their Stability Assessment of the Structure of the Solid/Liquid Interface Assessment of the State of the Dispersion Bulk Properties of Suspensions Equilibrium Sediment Volume (or Height) and Redispersion Rheological Measurements Assessment of Sedimentation Assessment of Flocculation Time Effects during Flow Thixotropy Constant Stress (Creep) Experiments Dynamic (Oscillatory) Measurements Sedimentation of Suspensions and Prevention of Formation of Dilatant Sediments (Clays) Prevention of Sedimentation and Formation of Dilatant Sediments Balance of the Density of the Disperse Phase and Medium Reduction of Particle Size Use of High Molecular Weight Thickeners Use of Inert Fine Particles Use of Mixtures of Polymers and Finely Divided Particulate Solids Depletion Flocculation Use of Liquid Crystalline Phases 255 References 256

11 XII Contents 8 Surfactants in Foams Introduction Foam Preparation Foam Structure Classification of Foam Stability Drainage and Thinning of Foam Films Drainage of Horizontal Films Drainage of Vertical Films Theories of Foam Stability Surface Viscosity and Elasticity Theory Gibbs Marangoni Effect Theory Surface Forces Theory (Disjoining Pressure) Stabilisation by Micelles (High Surfactant Concentrations > c.m.c.) Stabilization by Lamellar Liquid Crystalline Phases Stabilisation of Foam Films by Mixed Surfactants Foam Inhibitors Chemical Inhibitors that Both Lower Viscosity and Increase Drainage Solubilised Chemicals that Cause Antifoaming Droplets and Oil Lenses that Cause Antifoaming and Defoaming Surface Tension Gradients (Induced by Antifoamers) Hydrophobic Particles as Antifoamers Mixtures of Hydrophobic Particles and Oils as Antifoamers Physical Properties of Foams Mechanical Properties Rheological Properties Electrical Properties Electrokinetic Properties Optical Properties Experimental Techniques for Studying Foams Techniques for Studying Foam Films Techniques for Studying Structural Parameters of Foams Measurement of Foam Drainage Measurement of Foam Collapse 283 References Surfactants in Nano-Emulsions Introduction Mechanism of Emulsification Methods of Emulsification and the Role of Surfactants Preparation of Nano-Emulsions Use of High Pressure Homogenizers Phase Inversion Temperature (PIT) Principle 291

12 Contents XIII 9.5 Steric Stabilization and the Role of the Adsorbed Layer Thickness Ostwald Ripening Practical Examples of Nano-Emulsions 298 References Microemulsions Introduction Thermodynamic Definition of Microemulsions Mixed Film and Solubilisation Theories of Microemulsions Mixed Film Theories Solubilisation Theories Thermodynamic Theory of Microemulsion Formation Reason for Combining Two Surfactants Free Energy of Formation of Microemulsion Factors Determining W/O versus O/W Microemulsions Characterisation of Microemulsions Using Scattering Techniques Time Average (Static) Light Scattering Calculation of Droplet Size from Interfacial Area Dynamic Light Scattering (Photon Correlation Spectroscopy) Neutron Scattering Contrast Matching for Determination of the Structure of Microemulsions Characterisation of Microemulsions Using Conductivity, Viscosity and NMR 328 References Role of Surfactants in Wetting, Spreading and Adhesion General Introduction Concept of Contact Angle Contact Angle Wetting Line Three-phase Line (Solid/Liquid/Vapour) Thermodynamic Treatment Young s Equation Adhesion Tension Work of Adhesion W a Work of Cohesion Calculation of Surface Tension and Contact Angle Good and Girifalco Approach Fowkes Treatment Spreading of Liquids on Surfaces Spreading Coefficient S Contact Angle Hysteresis Reasons for Hysteresis Critical Surface Tension of Wetting and the Role of Surfactants Theoretical Basis of the Critical Surface Tension Effect of Surfactant Adsorption 351

13 XIV Contents Measurement of Contact Angles Sessile Drop or Adhering Gas Bubble Method Wilhelmy Plate Method Capillary Rise at a Vertical Plate Tilting Plate Method Capillary Rise or Depression Method Dynamic Processes of Adsorption and Wetting General Theory of Adsorption Kinetics Adsorption Kinetics from Micellar Solutions Experimental Techniques for Studying Adsorption Kinetics Wetting Kinetics Dynamic Contact Angle Effect of Viscosity and Surface Tension Adhesion Intermolecular Forces Responsible for Adhesion Interaction Energy Between Two Molecules Mechanism of Adhesion Deposition of Particles on Surfaces Van der Waals Attraction Electrostatic Repulsion Effect of Polymers and Polyelectrolytes on Particle Deposition Effect of Nonionic Polymers on Particle Deposition Effect of Anionic Polymers on Particle Deposition Effect of Cationic Polymers on Particle Deposition Particle Surface Adhesion Surface Energy Approach to Adhesion Experimental Methods for Measurement of Particle Surface Adhesion Role of Particle Deposition and Adhesion in Detergency Wetting Removal of Dirt Prevention of Redeposition of Dirt Particle Deposition in Detergency Particle Surface Adhesion in Detergency 396 References Surfactants in Personal Care and Cosmetics Introduction Lotions Hand Creams Lipsticks Nail Polish Shampoos Antiperspirants Foundations 401

14 Contents XV 12.2 Surfactants Used in Cosmetic Formulations Cosmetic Emulsions Manufacture of Cosmetic Emulsions Nano-Emulsions in Cosmetics Microemulsions in Cosmetics Liposomes (Vesicles) Multiple Emulsions Polymeric Surfactants and Polymers in Personal Care and Cosmetic Formulations Industrial Examples of Personal Care Formulations and the Role of Surfactants Shaving Formulations Bar Soaps Liquid Hand Soaps Bath Oils Foam (or Bubble) Baths After-Bath Preparations Skin Care Products Hair Care Formulations Sunscreens Make-up Products 430 References Surfactants in Pharmaceutical Formulations General Introduction Thermodynamic Consideration of the Formation of Disperse Systems Kinetic Stability of Disperse Systems and General Stabilisation Mechanisms Physical Stability of Suspensions and Emulsions Surfactants in Disperse Systems General Classification of Surfactants Surfactants of Pharmaceutical Interest Physical Properties of Surfactants and the Process of Micellisation Size and Shape of Micelles Surface Activity and Adsorption at the Air/Liquid and Liquid/Liquid Interfaces Adsorption at the Solid/Liquid Interface Phase Behaviour and Liquid Crystalline Structures Electrostatic Stabilisation of Disperse Systems Van der Waals Attraction Double Layer Repulsion Total Energy of Interaction Steric Stabilization of Disperse Systems 447

15 XVI Contents Adsorption and Conformation of Polymers at Interfaces Interaction Forces (Energies) Between Particles or Droplets Containing Adsorbed Non-ionic Surfactants and Polymers Criteria for Effective Steric Stabilisation Surface Activity and Colloidal Properties of Drugs Association of Drug Molecules Role of Surface Activity and Association in Biological Efficacy Naturally Occurring Micelle Forming Systems Biological Implications of the Presence of Surfactants in Pharmaceutical Formulations Aspects of Surfactant Toxicity Solubilised Systems Experimental Methods of Studying Solubilisation Pharmaceutical Aspects of Solubilisation Pharmaceutical Suspensions Main Requirements for a Pharmaceutical Suspension Basic Principles for Formulation of Pharmaceutical Suspensions Maintenance of Colloid Stability Ostwald Ripening (Crystal Growth) Control of Settling and Prevention of Caking of Suspensions Pharmaceutical Emulsions Emulsion Preparation Emulsion Stability Lipid Emulsions Perfluorochemical Emulsions as Artificial Blood Substitutes Multiple Emulsions in Pharmacy Criteria for Preparation of Stable Multiple Emulsions Preparation of Multiple Emulsions Formulation Composition Characterisation of Multiple Emulsions Liposomes and Vesicles in Pharmacy Factors Responsible for Formation of Liposomes and Vesicles The Critical Packing Parameter Concept Solubilisation of Drugs in Liposomes and Vesicles and their Effect on Biological Enhancement Stabilisation of Liposomes by Incorporation of Block Copolymers Nano-particles, Drug Delivery and Drug Targeting Reticuloendothelial System (RES) Influence of Particle Characteristics Surface-modified Polystyrene Particles as Model Carriers Biodegradable Polymeric Carriers Topical Formulations and Semi-solid Systems Basic Characteristics of Semi-Solids Ointments Semi-Solid Emulsions 496

16 Contents XVII Gels 497 References Applications of Surfactants in Agrochemicals Introduction Emulsifiable Concentrates Formulation of Emulsifiable Concentrates Spontaneity of Emulsification Fundamental Investigation on a Model Emulsifiable Concentrate Concentrated Emulsions in Agrochemicals (EWs) Selection of Emulsifiers Emulsion Stability Characterisation of Emulsions and Assessment of their Long-term Stability Suspension Concentrates (SCs) Preparation of Suspension Concentrates and the Role of Surfactants Wetting of Agrochemical Powders, their Dispersion and Comminution Control of the Physical Stability of Suspension Concentrates Ostwald Ripening (Crystal Growth) Stability Against Claying or Caking Assessment of the Long-term Physical Stability of Suspension Concentrates Microemulsions in Agrochemicals Basic Principles of Microemulsion Formation and their Thermodynamic Stability Selection of Surfactants for Microemulsion Formulation Characterisation of Microemulsions Role of Microemulsions in Enhancement of Biological Efficacy Role of Surfactants in Biological Enhancement Interactions at the Air/Solution Interface and their Effect on Droplet Formation Spray Impaction and Adhesion Droplet Sliding and Spray Retention Wetting and Spreading Evaporation of Spray Drops and Deposit Formation Solubilisation and its Effect on Transport Interaction Between Surfactant, Agrochemical and Target Species 591 References Surfactants in the Food Industry Introduction Interaction Between Food-grade Surfactants and Water Liquid Crystalline Structures 596

17 XVIII Contents Binary Phase Diagrams Ternary Phase Diagrams Proteins as Emulsifiers Interfacial Properties of Proteins at the Liquid/Liquid Interface Proteins as Emulsifiers Protein Polysaccharide Interactions in Food Colloids Polysaccharide Surfactant Interactions Surfactant Association Structures, Microemulsions and Emulsions in Food Effect of Food Surfactants on the Rheology of Food Emulsions Interfacial Rheology Bulk Rheology Rheology of Microgel Dispersions Food Rheology and Mouthfeel Mouth Feel of Foods Role of Rheology Break-up of Newtonian Liquids Break-up of Non-Newtonian Liquids Complexity of Flow in the Oral Cavity Rheology Texture Relationship Practical Applications of Food Colloids 626 References 629 Subject Index 631

18 XIX Preface Surfactants find applications in almost every chemical industry, such as in detergents, paints, dyestuffs, paper coatings, inks, plastics and fibers, personal care and cosmetics, agrochemicals, pharmaceuticals, food processing, etc. In addition, they play a vital role in the oil industry, e.g. in enhanced and tertiary oil recovery, oil slick dispersion for environmental protection, among others. This book has been written with the aim of explaining the role of surfactants in these industrial applications. However, in order to enable the chemist to choose the right molecule for a specific application, it is essential to understand the basic phenomena involved in any application. Thus, the basic principles involved in preparation and stabilization of the various disperse systems used namely emulsions, suspensions, microemulsions, nano-emulsions and foams need to be addressed in the various chapters concerned with these systems. Furthermore, it is essential to give a brief description and classification of the various surfactants used (Chapter 1). The physical chemistry of surfactant solutions and their unusual behavior is described in Chapter 2. Particular attention was given to surfactant mixtures, which are commonly used in formulations. Chapter 3 gives a brief description of the phase behavior of surfactant solutions plus a description of the various liquid crystalline phases formed. The adsorption of surfactants at the air/liquid and liquid/liquid interface is described in Chapter 4, with a brief look at the experimental techniques that can be applied to measure the surface and interfacial tension. The adsorption of surfactants on solid surfaces is given in Chapter 5, with special attention given to the adsorption of polymeric surfactants, which are currently used for the enhanced stabilization of emulsions and suspensions. The use of surfactants for preparation and stabilization of emulsions is described in Chapter 6, paying particular attention to the role of surfactants in the preparation of emulsions and the mechanisms of their stabilization. The methods that can be applied for surfactant selection are also included, as is a comprehensive section on the rheology of emulsions. Chapter 7 describes the role of surfactants in preparation of suspensions and their stabilization, together with the methods that can be applied to control the physical stability of suspensions. A section has been devoted to the rheology of suspensions with a brief description of the techniques that can be applied to study their flow characteristics. Chapter 8 describes the role of surfactants in foam formation and its stability. Chapter 9 deals with the role of surfactants in formation and stabilization of nano-emulsions the latter having recently been Applied Surfactants: Principles and Applications. Tharwat F. Tadros Copyright WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim ISBN:

19 XX Preface applied in personal care and cosmetics as well as in health care. The origin of the near thermodynamic stability of these systems is adequately described. Chapter 10 deals with the subject of microemulsions, the mechanism of their formation and thermodynamic stability, while Chapter 11 deals with the topic of the role of surfactants in wetting, spreading and adhesion. The surface forces involved in adhesion between surfaces as well as between particles and surfaces are discussed in a quantitative manner. Chapters 12 to 15 deal with some specific applications of surfactants in the following industries: personal care and cosmetics, pharmaceuticals, agrochemicals and the food industry. These chapters have been written to illustrate the applications of surfactants, but in some cases the basic phenomena involved are briefly described with reference to the more fundamental chapters. This applied part of the book demonstrates that an understanding of the basic principles should enable the formulation scientist to arrive at the optimum composition using a rational approach. It should also accelerate the development of the formulation and in some cases enable a prediction of the long-term physical stability. In writing this book, I was aware that there are already excellent texts on surfactants on the market, some of which address the fundamental principles, while others are of a more applied nature. My objective was to simplify the fundamental principles and illustrate their use in arriving at the right target. Clearly the fundamental principles given here are by no means comprehensive and I provide several references for further understanding. The applied side of the book is also not comprehensive, since several other industries were not described, e.g. paints, paper coatings, inks, ceramics, etc. Describing the application of surfactants in these industries would have made the text too long. I must emphasize that the references given are not up to date, since I did not go into much detail on recent theories concerning surfactants. Again an inclusion of these recent principles would have made the book too long and, in my opinion, the references and analysis given are adequate for the purpose of the book. Although the text was essentially written for industrial scientists, I believe it could also be useful for teaching undergraduate and postgraduate students dealing with the topic. It could also be of use to research chemists in academia and industry who are carrying out investigations in the field of surfactants. Berkshire, January 2005 Tharwat Tadros